Coke is a solid carbon fuel and carbon source used to melt and reduce iron ore in the production of steel. During an iron-making process, iron ore, coke, heated air and limestone or other fluxes are fed into a blast furnace. The heated air causes combustion of the coke that provides heat and a source of carbon for reducing iron oxides to iron. Limestone or other fluxes may be added to react with and remove the acidic impurities, called slag, from the molten iron. The limestone-impurities float to the top of the molten iron and are skimmed off.
In one process, known as the “Thompson Coking Process,” coke used for refining metal ores, as described above, is produced by batch feeding pulverized coal to an oven that is sealed and heated to very high temperatures for 24 to 48 hours under closely controlled atmospheric conditions. Coking ovens have been used for many years to covert coal into metallurgical coke. During the coking process, finely crushed coal is heated under controlled temperature conditions to devolatilize the coal and form a fused mass having a predetermined porosity and strength. Because the production of coke is a batch process, multiple coke ovens are operated simultaneously, hereinafter referred to as a “coke oven battery”.
At the end of the coking cycle, the finished coke is removed from the oven and quenched with water. The cooled coke may be screened and loaded onto rail cars or trucks for shipment or later use or moved directly to an iron melting furnace.
The melting and fusion process undergone by the coal particles during the heating process is the most important part of the coking process. The degree of melting and degree of assimilation of the coal particles into the molten mass determine the characteristics of the coke produced. In order to produce the strongest coke from a particular coal or coal blend, there is an optimum ratio of reactive to inert entities in the coal. The porosity and strength of the coke are important for the ore refining process and are determined by the coal source and/or method of coking.
Coal particles or a blend of coal particles are charged into hot ovens on a predetermined schedule, and the coal is heated for a predetermined period of time in the ovens in order to remove volatiles from the resulting coke. The coking process is highly dependent on the oven design, the type of coal and conversion temperature used. Ovens are adjusted during the coking process so that each charge of coal is coked out in approximately the same amount of time. Once the coal is coked out, the coke is removed from the oven and quenched with water to cool it below its ignition temperature. The quenching operation must also be carefully controlled so that the coke does not absorb too much moisture. Once it is quenched, the coke is screened and loaded into rail cars or trucks for shipment.
Because coal is fed into hot ovens, much of the coal feeding process is automated. In slot-type ovens, the coal is typically charged through slots or openings in the top of the ovens. Such ovens tend to be tall and narrow. More recently, horizontal non-recovery or heat recovery type coking ovens have been used to produce coke. Horizontal ovens are described for example in U.S. Pat. Nos. 3,784,034 and 4,067,462 to Thompson. In the non-recovery or heat recovery type coking ovens, conveyors are used to convey the coal particles horizontally into the ovens to provide an elongate bed of coal having a height of about 101 centimeters, a length of about 13.7 meters, and a width of about 3.6 meters.
As the source of coal suitable for forming metallurgical coal has decreased, attempts have been made to blend weak or non-coking coals with coking coals to provide a suitable coal charge for the ovens. One attempt is to use compacted coal. The coal may be compacted before or after it is in the oven. While coal conveyors are suitable for charging ovens with particulate coal that is then partially compacted in the oven, such conveyors are generally not suitable for charging ovens with pre-compacted coal. Ideally, the coal should be compacted to greater than 800 kilograms per cubic meter in order to enhance the usefulness of lower quality coal. It is well known that as the percentage of lower quality coal in a coal blend is increased, higher levels of coal compaction are required up to about 1040 to 1120 kilograms per cubic meter.
However, currently available processes are not suitable for providing a compacted coal charge that has a substantially uniform bulk density throughout the entire depth of an elongate coal charge bed at a relatively high rate of speed and without the generation of substantial amounts of coal dust during compaction. There is a need therefor, for an improved method and apparatus for compacting coal without generating coal dust and for charging coking ovens with pre-compacted coal. There is also a need for an apparatus for minimizing the amount of time required to provide a substantially uniform bed of compacted coal for use in making metallurgical coke.
In accordance with the foregoing and other needs, the disclosure provides relatively high speed methods for increasing the bulk density of coal particles without impacting the coal particles and an apparatus for compacting coal for making metallurgical coke. The method includes depositing coal particles onto a charging plate external to a coking oven. The charging plate has side walls, and at least one movable end wall to provide an elongate bed of dry, uncompacted coal having an upper surface on the charging plate. The uncompacted coal is compacted by passing a vibratory cylindrical compactor along a length of the uncompacted coal for a number of passes sufficient to decrease a thickness of the bed of coal to less than about 80 percent of an original thickness of the uncompacted coal. The vibratory cylindrical compactor has a length to diameter ratio ranging from about 1.4:1 to about 2:1. In another aspect, an exemplary embodiment of the disclosure provides a coal compacting and coke oven charging apparatus. The apparatus has a coal bed transfer plate having side walls, at least one movable end wall, and a transfer plate translating mechanism for transporting compacted coal into the coke oven. A vacuum source is used for degassing the uncompacted bed of coal during the compaction process to provide a dry, compacted coal bed having a bulk density ranging from about 960 to about 1200 kilograms per cubic meter.
In yet another aspect, an exemplary embodiment of the disclosure provides a coal compacting and coke oven charging apparatus The apparatus includes a coal bed charge car comprising a transfer plate having side walls, at least one movable end wall, and a transfer plate translating mechanism for transporting compacted coal into the coke oven. A coal compacting device is provided to compact the coal without impact energy. The coal compacting device includes a vibratory roller mechanism for compacting a bed of uncompacted coal on the transfer plate; a coal bed translation device attached to the vibratory roller mechanism for moving the vibratory roller mechanism along a length of the bed of uncompacted coal; an elevation mechanism on the coal bed translation device for lowering the vibratory roller to be in contact with the uncompacted coal during a compacting step and for raising the vibratory roller out of contact with compacted coal during an oven charging step; and a degassing device for degassing the uncompacted bed of coal during the compacting step.
The method and apparatus described herein provide unique advantages for coking operations including providing coal with a relatively high bulk density in a relatively short period of time. Another advantage of the method and apparatus is that relatively simple mechanical devices may be used to compact the coal and transfer the compacted coal into the coke oven without using a pile-driver-type compaction device that may cause an increase in coal dust during compaction and that may cause damage to structures and equipment during the compaction process. A further advantage is that the resulting coal bed is substantially compacted throughout its depth to about the same uniform bulk density.